The long-term research objective is to understand the mechanism by which excitatory and inhibitory neurotransmitter receptors regulate signal transmission between the billions of cells in the mammalian central nervous system (CNS). It is also to understand the effects of neurological diseases and therapeutic compounds and abused drugs on the mechanism. To achieve these objectives, we have developed rapid chemical reaction techniques suitable for investigations of cell surface receptors in the mu s-to-ms time domain. One of these is a laser-pulse photolysis technique. We have achieved this goal with three of the main types of neurotransmitter receptors. Here we plan to extend the laser-pulse photolysis technique to the remaining two major types of neurotransmitter receptors in the CNS, the glycine and serotonin 5-HT receptors. In the laser-pulse photolysis technique, receptor-containing cells are pre- equilibrated with a photolabile inert precursor of a neurotransmitter (caged neurotransmitter); the neurotransmitter is released by a light pulse, and the resulting whole-cell current, due to the opening of receptor-channels, is recorded and analyzed. Central to this development is the availability of caged neurotransmitters that are photolyzed in microseconds and are biologically inert. One immediate aim is to develop caged glycine and caged serotonin. In the case of serotonin this requires the development of a caging group that is photolyzed in the visible wavelength region because serotonin is photodamaged at the wavelengths used previously to cage other neurotransmitters. Such a group will allow the use of inexpensive and simple-to-use light sources and make the technique accessible to other investigators, thereby accelerating progress in this field. A second aim is to determine the difference in channel-opening mechanism between a normal glycine receptor and a mutant form found in hyperekplexia/startle disease. A third aim is to investigate the mechanism of the channel-opening process of the serotonin 5-HT3 receptor and the effect of therapeutic agents on this mechanism.